The invention relates generally to fibrous materials and more specifically to fibrous materials made from wood products. The invention further relates to a blend of materials composed of Fiberized fibers and refined fibers exhibiting both high bulk and high strength. The invention further relates to processes that permanently change fiber morphology of a Fiberized wood fiber resulting in unchanging high bulk, maximized surface area, low density wood fiber products. Such properties arise from the permanent nature of the kink, twist, curl, crimp or other curvilinear deformations formed into the fiber. The blended fibers of the invention can be used in tissue, distribution layers, filter papers, and other applications where high bulk, high surface area, low density arising from the fiber morphology can be beneficially used.
The use of steam or explosive decompression to disintegrate wood fibers is well-known in the art. For example, Mason discloses the general techniques of steam explosion treatments in Mason""s U.S. Pat. Nos. 1,586,159; 1,578,609; 1,655,618; 1,824,221; 1,872,996; and 1,922,313. All of these patents are directed generally to the disintegration of primary cellulosic materials such as wood chips.
Later patents disclose incremental improvements and refinements in steam explosion treatments. For example, U.S. Pat. No. 2,516,847 to Boehm is directed to a means of sizing the exploded fibers. Mitscherling, U.S. Pat. No. 1,793,711, teaches use of a vacuum source to remove volatile resins prior to the pressurization and explosive decompression treatment by adding a series of explosive steps. Apparently this serves to more evenly disintegrate the fibers. This series of explosive steps permits the use of lower pressures and temperatures.
Mamers, et al., U.S. Pat. No. 4,163,687, is directed to a uniquely designed nozzle for assisting the liberation of fibers from cellulosic material during explosive defibration. The nozzle has a plurality of internal bars which form a tortuous path through which material must pass. O""Connor, U.S. Pat. No. 3,707,436, discloses using ammonia instead of steam. Apparently compounds such as ammonia are effective at swelling and plasticizing wood. Morgan, U.S. Pat. No. 2,234,188, is directed to production of light-colored cellulosic fiber. This is accomplished by first treating the chips or other small pieces of wood with an alkaline sulphite of alkaline metal such as sodium sulphite or potassium sulphite.
U.S. Pat. No. 4,488,932, to Robert J. Eber et al. discloses improved bulk and softness produced by using fiberized fibers. However, the curls and kinks relax significantly during the wet-forming process. As a result, the patent described the foam-forming process to make tissue. The fiberized fibers are dispersed in an aqueous foam which minimizes water absorption and, consequently, the reversal of the treated fibers to their original form.
U.S. Pat. No. 5,102,501, also to Robert J. Eber et al. discloses improving bulk and softness by depositing the fiberized fibers on the forming wire and dewatered in a period of time sufficiently shorter so that the fiberized fibers preserve their bulk-enhancing characteristics.
However, while past efforts have resulted in methods of controlling size, absorbance, and bulking characteristics, there is little, if any, teaching on methods useful in enhancing and preserving the curl and kink characteristics of the fiberized fibers. In addition, nothing in the past suggests that blending the fiberized/steam exploded fibers with highly refined fibers will form a sheet with higher bulk without losing strength.
Therefore, a need remains for a material which exhibits high bulk while retaining high strength.
In accordance with a first aspect of the invention there is provided a process for the production of a fiber having a permanently modified fiber morphology. The process includes:
(a) subjecting a papermaking fiber to mechanical deformation without substantial fiber breakage resulting in the fiber having a transient fiber morphology having a curl index of at least 0.15;
(b) subjecting the fiber with the transient fiber morphology to a treatment with steam at super atmospheric temperature and pressure for a sufficient period of time to render the fiber morphology permanent; and
(c) explosively releasing the super atmospheric steam pressure.
The fiber resulting from this process has a permanent curl index of at least 0.2.
Another aspect of the invention is a process for the production of a fiber having a permanently modified fiber morphology. The process includes:
(a) subjecting a papermaking fiber to hammermilling without substantial fiber breakage resulting in a fiber with a curvilinear structure having a curl index of at least 0.2;
(b) subjecting the fiber with the curvilinear structure to treatment with steam at super atmospheric temperature and pressure for about 0.5 minutes to about 20 minutes, thus rendering the fiber morphology permanent; and
(c) explosively releasing the super atmospheric steam pressure.
The fiber resulting from this process has a permanent curl index of at least 0.2.
Another aspect of the invention is an improved fiber material having increased bulk, which includes a blend of fibers having a permanent fiber morphology with a curl index of at least 0.2. This modified fiber is the product of the process of first mechanically deforming a papermaking wood fiber and subjecting the resulting fiber to steam at super atmospheric temperature and pressure to obtain the permanent fiber morphology. This modified fiber is blended with a refined papermaking wood fiber. There is about 0.01 to about 100 parts of the fiber having a permanent fiber morphology per each one part by weight of the refined papermaking fiber. This improved fiber material has a bulk greater than 3.0 cm3/g.
The fiber material can form sheets with high bulk and high strength. This fiber material could be used in tissue, towel or saturation paper basesheets. In addition, this material could be used as wicking distribution material. The invention is further directed to a fiber material which is created from a blend of Fiberized and refined fibers.